[R-390] The OD discussion

[ken]

Roy Morgan wrote:
>
> On Dec 16, 2008, at 11:33 PM, ken wrote:
>> Sorry Roy, my apologies...I was thinking of something entirely 
>> different.
>
> Goodness.. may be the first time that ever happened to you?  I can't 
> remember it ever happening.. Now, what was I thinking about... hehehe

Yes..hehehe...it seems to happen to me more and more these days!
>> ...two obvious faults...
>> Low sensitivity below 8mhz and distorted audio with the noise limiter 
>> turned off
>
> If I had a radio with those things going on, I'd first check the 
> activity of the 17 mc crystal.  Easiest way is to substitute a wee 
> oven from another radio.  I can't remember if there is a test point at 
> the grid of the mixer that oscillator feeds, but if there is, test for 
> correct DC level.  (Use a 100k or 1 meg resistor if you use a modern 
> DMM with not isolating resistor in the probe.)
Thanks for the tip regarding the 17mHz crystal...I can swap them around 
from the other 390As that I have here, so that will be easy to check. 
The sensitivity issues below 8 mHz can also be caused by C-327 on the RF 
deck.
>
> The noise limiter thing is less easy for me to guess about since I 
> never had that... new tube first, then circuit voltages.
The noise limiter problem can also be caused by the failure of C-536, 
the plate bypass capacitor for the noise limiter tube.
>
> I have sooo many radios in waiting here.. some of them not seen for a 
> very long time!
>
I have a total of six BAs and I decided to box them all up except 
one...I am not going to play with any other radios until the one that's 
unboxed is completely finished. Then I'll unbox another one and start 
work on that until they are all done. An early New Years resolution for 
me is to complete at least one full restoration per year...sounds like a 
long time (it is!) but with my mentality on component choices I'll be 
working when the budget allows.

73s
Ken